Eric Mangini’s walk came on a gangplank, a day after the Jets completed a 9-7 season that sure felt like 6-10, little more than a month after they were 8-3 and forcing even their most cynical supporters to re-think their skeptical ways. This was a firing earned on merit, and underachievement, and the paranoid police state Mangini constructed around his team.

Firings are never easy. But in this case, it was the only easy part.

What follows now, for owner Woody Johnson and for GM Mike Tannenbaum, is the hard part, the tricky part, the task that past performance warns us neither man may be equal to – which yesterday’s public performance did nothing to dispel.

Tannenbaum kept talking about the “foundation” that is in place here, and if what you’re looking for in a foundation is one in which a team’s character evaporates in the important hours of a season, then he is right, there is a Rock of Gibraltar growing in Florham Park. Johnson, even more troublingly, talked about Year Two of the Brett Favre Experience, still sounding as if he is caught in the throes of puppy love.

These are not good signs. Because what Johnson and Tannenbaum need to do, more than anything, in the coming days and weeks will involve coming to terms with the fact that the only way to fix the Jets, as currently constituted, is to go with known entities. This is not a team, or a time, for taking another flier on another flavor-of-the-month coordinator. Giantss defensive coordinator Steve Spagnuolo is a wonderful coach, a popular name, sure to be an in-demand interview; so, once upon a time, were Romeo Crennel, Dave Wannstedt and Mike Martz. And Eric Mangini.

No, the Jets need to swim in the adult pool this time around. That means investigating immediately whether it is true that Bill Cowher – whose daughter, serendipitously, attends Princeton – would ponder an offer to leave his cushy retirement if the Jets would be willing to fork over, say, five years and $40 million. That would also mean Johnson having to inform Tannenbaum that his vise-like control on personnel matters will be loosened, if not removed. Johnson hinted he wasn’t at all interested in that kind of restructuring yesterday. That is unfortunate.

And that leaves three other established names that are very much available: Marty Schottenheimer, Brian Billick and Mike Holmgren. None presently own the kind of leverage that would hammer Tannenbaum out of the picture; all possess a level of gravitas that would make it imperative that they, not Johnson or Tannenbaum, would have final say on who their quarterback would be next year.

More important, all boast the same kind of winning resume that the Jets are now desperate for; Billick and Holmgren wear Super Bowl rings, while Schottenheimer (whose playoff heartbreaks are legendary) has won 61 percent of his regular-season games. Billick can be prickly with the media, which some have seen as a potential downfall in New York, but he seems to have a lot of Bobby Valentine in him, which could be as much a benefit as a detriment.

The Jets have led the world in hiring first-time pro coaches, from their very first, Sammy Baugh, to Mangini, 10 out of 14 in all. From Bulldog Turner and Bruce Coslet to Herman Edwards and Al Groh. It is no coincidence that the only coaches to have any measure of real success with the team, Weeb Ewbank and Bill Parcells, had each won two NFL championships apiece before roaming the Jets’ sidelines.

“New York is a hell of a place to do on-the-job training,” one of those erstwhile New York newbies, Pete Carroll, said a few years ago.

We already knew that. What’s vital is that Johnson and Tannenbaum know that, and are willing to make the concessions – and sacrifices – necessary to fix what’s broken. Otherwise what they did yesterday simply will be the worst kind of window dressing, sacrificing a career in the name of fan outrage and personal seat licenses.